Head-mounted and head-up displays for simulation, training, entertainment, and military applications have been in use for a number of years. They have a great potential for construction work, sports, space suit, medicine, education, mobile communications and for other fields. Substantial efforts are made to reduce size, weight, cost, and the number of optical and electronic elements of a display. Further efforts are made to improve brightness, contrast, and image quality.
A head-mounted display (HMD) can use a micro-display source such as a liquid crystal display (LCD) or liquid crystal on silicon (LCOS) with a backlight. An alternative is to use an organic light-emitting diode (OLED) display, reflective and/or refractive optics to create a magnified virtual image of the micro-display source for a viewer's eye(s). A number of opaque head-mounted displays have been developed.
But none of them has allowed users to see through to the real world, severely limiting possible applications. [O. Cakmakci, J. Rolland, Head-Worn Displays: A Review, J. Display Technology, Vol. 2(3), pp. 199-216 (2006)]. Partially see-through head-mounted displays exist. They use an optical combiner element in front of the viewer's eyes to allow for superposition of an external view with the virtual imagery. These partially-see-through head-mounted displays suffer from poor light transmission through the combiner resulting in a dim view of the outside world and decreased virtual image brightness.
There has been a long-felt need for a viable optical see-through head-mounted display offering minimization of the size of the optics. Using the display in combination with the environment would permit creating a synthetic environment that is a combination of the display image and the environment. See-through head-mounted displays can advantageously be deployed as goggles that are lightweight. Further it would be advantageous for them to provide with sufficient eye space (eye relief) to permit the wearing correction prescription glasses and have sufficient eye box to provide a full field-of-view (FOV) image at significant eye movements.
An edge-illuminated substrate holographic approach with a single hologram for see-through image creation was proposed J. Upatnieks, ‘Compact Holographic Sight’, Proc. SPIE, Vol. 883, pp. 171-176 (1988). Such approach indeed allowed for a see-through imagery with a simultaneous bright view of the outside world. But the image quality was poor, mostly because of the color dispersion created by a single hologram for a broad-band source. A single-hologram approach was followed by some developers. M. Simmonds, M. Valera, ‘Projection Display’ US Pat. Application 2009/0190222 A1 (43) (2009); T. Takeyama, ‘Observation Optical system’, U.S. Pat. No. 6,636,356 B2 (2003); Yu. Ouchi, ‘Image Combiner and Image Display Unit’, U.S. Pat. No. 7,072,085 B2 (2006); I. Kasai, ‘Image Display Device’, U.S. Pat. No. 6,429,954 B1 (2002). They used either a single laser source for LCD illumination thus not enabling the color imagery or proposed very complicated hologram recording geometries for generating aspheric recording wave-fronts which are rather complicated and costly to be implemented in practice.
Another approach uses diffractive elements placed on a transparent waveguide to create an enlarged see-through virtual image for a viewer. P. Repetto, E. Borello, S. Bernard, ‘Light Guide for Display Devices of the Head-Mounted or Head-up Type’, U.S. Pat. No. 6,825,987 B2 (2004); T. Levola, Method and Optical System for Coupling Light Into a Waveguide, U.S. Pat. No. 7,181,108 B2 (2007); Y-R. Song, ‘Wearable Display System Adjusting Magnification of an Image’, US Pat. Application US2004/0004767 A1 (2004). While providing a see-through capability, such an approach suffers from stray light generated by unwanted diffraction into undesired diffractive orders that substantially decreases the image quality and contrast.
Another approach uses partially reflective elements placed at some angle on a transparent waveguide. Ya. Amitai, ‘Substrate-Guided Optical Beam Expander’, U.S. Pat. No. 6,829,095 B2 (2004). While creating a see-through imagery, fabrication of such elements in mass quantities can be prohibitively expensive.
In an attempt to remove the color dispersion from the imagery, another approach was followed that uses two coupled holograms for a see-through image creation Y. Amitai, A. Friesem, I. Shariv, ‘Planar Holographic Optical Device for Beam Expansion and Display’, U.S. Pat. No. 6,169,613 B1 (2001); H. Mukawa, ‘Optical Device and Virtual Image Display’, U.S. Pat. No. 7,453,612 (2008); H. Mukawa, K. Akutsu, ‘Optical Device and Virtual Image Display Device’, U.S. Pat. No. 7,418,170 (2008). While providing a means to mostly remove the color dispersion from the imagery for the case when two identical holographic gratings are placed mirror-symmetrically on the waveguide, the actually achieved field-of-view was rather narrow (˜15 deg). In addition, a path of creating such displays for curved substrates which, is needed for many applications was not outlined. Also, a desired reduction of the number of optical elements for such displays was not clarified.
There is therefore still a need for a display that uses a thin transparent waveguide that couples the light to the display in such a way as to create a wide field-of-view, aberration-free virtual image. It would be desirable for such a display to have a capability to provide a long (up to ˜70-80 mm) eye relief. It would be also desirable for the technology for the display to be capable of execution on a curved waveguide substrate so that it can conform with the shape of a helmet employed in e.g., avionic and in other applications, to allow for the implementation of compact optics, to provide a highly-transparent (˜90%) view of the outside world.
Embodiments of the invention can be used to evaluate surface mounted, portable or wearable gas detectors. Alternately, sensitivity parameters of various types of smoke detectors, or other types of detectors, can be evaluated. In yet another aspect of the invention, the hand held unit can communicate not only with the test device but also with an associated regional monitoring system.
We propose a display that uses a thin transparent waveguide with holographic elements enabling in-coupling and out-coupling of light to/from the waveguide in such a way as to create a wide field-of-view, aberration-free virtual image for a viewer, with a capability to provide a long (up to ˜70-80 mm) eye relief, with a capability to be formed on a curved waveguide substrate, desirably conformal with the shape of a helmet employed in e.g., avionic and in other applications, to allow for the implementation of compact optics, to provide a highly-transparent (˜90%) view of the outside world.